Publish Android releases to a self-hosted F-Droid repo

scripts/fdroid-publish.sh builds a signed arm64 APK and adds it to an
F-Droid repo in a given directory, creating the app signing key and the
repo on first use. The versionCode is the commit count, so any commit can
ship without a manual version bump.

Release builds are signed when src-tauri/gen/android/keystore.properties
exists and stay unsigned otherwise. The manifest picks up the deep-link
plugin's intent filter, which every build regenerates and was never
committed.

package.json

@@ -9,7 +9,8 @@
     "preview": "vite preview",
     "tauri": "tauri",
     "sync-server:build": "scripts/sync-server-image.sh build",
-    "sync-server:push": "scripts/sync-server-image.sh push"
+    "sync-server:push": "scripts/sync-server-image.sh push",
+    "android:publish": "scripts/fdroid-publish.sh"
   },
   "dependencies": {
     "@tauri-apps/api": "^2",